Believe it or not, I pulled up the hardwood floor in my bathroom and the subfloor is 1/4” plywood. If I put a good mortar on top of that plywood and use a 1/2” cement board on top of that, will that be a sufficient support for new tile? I’ll of course use more mortar over the cement board.

  • I'd be willing to bet that your subfloor is nominally 3/8" plywood (something like 11/32 actual). 1/4" just doesn't make sense (not that 3/8" is much better).
    – isherwood
    Apr 27 at 14:09

1 Answer 1


No, presuming this is not on a concrete slab.

Are you sure that the subfloor is 1/4"? I don't think you can even walk on that without going right through. I would think it is more likely an underlayment.

You need minimum of 3/4" subfloor with the cement board on top to ensure the deflection is not large enough for those tiles to quickly pop off from the flex. You really don't want anything less than 9/8" (1" and 1/8") of flooring under the tile and the floor should not really have a "bounce" to it.

I had an old house that I wanted to tile the kitchen in and had to reinforce the joists to get it stiff enough to do a 3/4" subfloor + cement board for the tiles, so it's not just about the subfloor/underlayment/cement board.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.